This invention relates to mechanical timing devices, and more particularly to such devices for automatically opening a parachute in response to a parachute opening signal.
It has long been necessary or desirable in certain instances to delay the opening of a parachute for a predetermined time period subsequent to an opening signal, such as automatic ejectment of a pilot from an aircraft in an emergency situation, to allow sufficient clearance between the opening parachute and the passing aircraft. Additionally, and especially in modern high-altitude flights, it has proven desirable to automatically preclude the opening of the parachute above a predetermined altitude so that the wearer fails quickly through the frigid, low-oxygen higher altitudes, unretarded by the parachute.
Various types of timing devices, both mechanical and explosive, have been employed to interpose such a time delay between the opening signal and the opening of the parachute. However, none have proven to be entirely satisfactory.
Many prior art mechanical timing devices (whether in combination with barometric lockouts or not) have employed complex, bulky and expensive mechanisms which are driven by and retard the opening movement of a spring-loaded parachute release cable. A common mechanism includes a rack in one form or another that is linked with the cable and which, upon release of the cable from a cocked position, is driven by the cable. The movement of the rack (and thus the cable) is retarded by its continuous engagement during its movement with a retarding gear train controlled by an escapement, governor wheel, or the like. Such devices, however, have little, if any, time delay adjustment capability and thus are of limited value where a wide range of easily adjustable time delays is desired. For instance, some of the prior art mechanical devices, despite their complexity, have but a single time delay available. Other prior art devices provide only a limited range of adjustment capabilities and have, at best, only a relatively short maximum time delay potential. Even the prior art devices which provide such limited adjustment potential require rather tedious adjustment procedures ranging from partial disassembly of the timing device, repositioning the internal timing mechanism, and reassembly of the device, to repositioning several external components.
Additionally, few, if any, prior art mechanical timing devices provide for accurate calibration of the actual time delay selected. Thus, for instance, in a prior art timing device having only a fixed time delay available, a variance in actual time delay from one device to another is unavoidable due to manufacturing variances in components.
The very complexity of prior art mechanical timing devices has resulted in devices which are unnecessarily bulky, heavy and expensive to manufacture. Similarly, the complexity of such devices renders them inordinately difficult to service and repair in many instances.
In an attempt to overcome the various problems presented by mechanical timing devices, devices employing delayed-burning explosive cartridges instead of mechanical delay mechanisms have been employed. Such devices commonly utilize spring-driven firing pins which are activated by the parachute opening signal to fire the explosive cartridge. The cartridges used are of a slow-burning type which have a built-in (and nonadjustable) firing delay. Upon firing, the cartridge typically activates a gas-driven piston which, in turn, is linked to a member which opens the parachute. While such explosive type delay mechanisms have proven to be less expensive to produce than their mechanical counterparts, they carry with them their own unique shortcomings which, to a great extent, offset their relative advantages.
A prime disadvantage of such explosive type time delay devices is that a given cartridge simply cannot be tested (either to determine that it will indeed fire, or if so, at exactly what time interval it will fire after being struck by the firing pin) and then reused. Further, unlike some of the more sophisticated prior art mechanical devices, no adjustability as to time delay is afforded by a given cartridge. To vary the desired time delay, another cartridge having a longer or shorter fixed time delay must be inserted into the device. This usually requires, at best, at least a partial disassembly and reassembly of the time delay device to insert a different cartridge (which may or may not be available to the parachute's user during flight).
Additionally, while usually somewhat less complex than mechanical timing devices, the cartridge type device carries with it the undesirable feature and potential hazard of requiring the user to continuously carry the explosive close to his body during flight.
In summary, none of the prior art devices (whether mechanical or explosive type) provide a time delay apparatus which combines the characteristics of low cost, ease and range of time delay adjustment, light weight and compactness, and high reliability. Accordingly, it is an object of this invention to provide a mechanical time delay device that eliminates or minimizes above-mentioned problems.